1. Technical Field
The present invention relates, in general, to an optical image stabilizer.
2. Description of the Related Art
As camera modules are having higher-resolution pixels and higher functionality, they are being applied to a wider variety of applications including mobile devices, such as mobile phones, notebook computers and tablet PCs. At the same time, as such applications are becoming smaller and slimmer, camera modules are becoming smaller and slimmer.
Furthermore, conventional autofocus (AF) camera modules are required to have only a group of lenses and an AF drive unit, which drives the lens group, or occasionally a location sensor for increasing the precision of the location of the lens group. Accordingly, such camera modules are rapidly becoming miniaturized and slimmed in relation to camera modules that have an optical image stabilizer (OIS).
That is, the OIS is required to have AF components as well as an OIS drive unit, which drives the lens group in two directions (typically X and Y directions; hereinafter, referred to as “X and Y directions”), which perpendicularly intersect the optical axis (Z axis). In order to increase the precision of the operation of the OIS, location sensors capable of measuring the location of the lens group are typically required in the two directions (X, Y), which perpendicularly intersect the optical axis (Z axis).
Accordingly, the miniaturization and slimness profile of the OIS may be determined by how the AF driving unit and the location sensors of the OIS are configured and arranged with the AF.
Two types of location sensors, including a Hall sensor and a photoreflector (PR) sensor, are widely used. The PR sensor radiates a predetermined amount of diffused light from the sensor itself, and then measures the amount or intensity of light that reflects from an opposing reflector plate and returns to the sensor. In this fashion, the PR sensor measures the location of the opposing reflector plate by detecting a variation in the amount or intensity of light that occurs when a relative displacement between the PR sensor and the opposing reflector plate occurs.
In addition, the Hall sensor causes a variation in a signal in response to a variation in magnetic force. Due to such characteristics, the Hall sensor has been widely used in measuring the location of the AF drive unit, which is constructed of magnets and coils. In the AF drive unit, which is generally constructed of magnets and coils, the magnets are used in such a way that they are opposed to the Hall sensor, or third magnets dedicated to the Hall sensor are additionally provided.
Here, since the size of the Hall sensor is currently being decreased, its use in a camera module including the OIS is gradually increasing.
However, the OIS is required to drive a group of lenses independently and respectively (without a mutual relationship) in the X and Y directions in response to vibration of the hand of a user. Therefore, there is a problem in that it is difficult to measure any displacement simultaneously in the X and Y directions using one Hall sensor.
That is, although one Hall sensor can measure the displacement in two axes depending on how the Hall sensor is fabricated, this type of Hall sensor is actually one Hall sensor chip into which two sensors are incorporated rather than a single Hall sensor. Accordingly, in fact, the Hall sensor does not greatly contribute to the miniaturization or slimness of the OIS.
In addition, the magnets opposing the Hall sensor are typically arranged such that predetermined gaps are maintained between the Hall sensor and the magnets. The Hall sensor is configured such that it can detect when a relative displacement occurs in the direction that perpendicularly intersects the direction of the gaps. Since the OIS is subjected to the miniaturization and slimness as described above, the importance of the arrangement of the Hall sensor and the magnets is further increasing.
The arrangement of the Hall sensor and the magnets in the related art is specifically disclosed in Patent Document 1 (U.S. Pat. No. 7,881,598 B1) and Patent Document 2 (US2011-0013895 A1). According to Patent Document 1, Hall sensors are mounted such that each Hall sensor is opposed to a corresponding magnet. A relative displacement is made without a variation in opposing gaps when the magnets are moved in the X and/or Y directions.
In addition, Patent Document 2 discloses optical image stabilization that is performed by tilting the entire AF module, to which a group of lenses and an image pickup device are coupled, in the opposite direction to the vibration of the hand.
In an example, when a displacement in the direction of a gap is detected from two Hall sensors, the tilt between the lens group and the image pickup device is calculated.
Furthermore, Patent Document 3 (KR0918816 B1) discloses a technique in which a PR sensor is employed instead of the Hall sensor, in which a location sensor is not opposed to magnets but to a component that acts as a reflector plate. Such a PR sensor measures the amount of a variation in the gap between the sensor and the reflector plate. If the reflector plate is sufficiently wide, there is no variation in a signal when the lens group is driven in the direction that intersects the direction of the gaps. Therefore, respective PR sensors, which are arranged along the X and Y axes, can perform measurement independently or without signal coupling.